Embodiments of the inventive concept relate to methods of measuring the phase of a phase shift mask and an apparatus performing such methods. More particularly, embodiments relate to a method of measuring the phase of a phase shift mask using extreme ultraviolet light, and an apparatus performing such methods.
The fabrication of contemporary semiconductor devices requires the use of many different fabrication processes. Some process types commonly used in the fabrication of densely integrated semiconductor devices employ a so-called phase shift mask. A phase shift mask includes a phase shift layer pattern which generally replaces the chrome layer used in other types of masks. For example, phase shift masks are commonly used in conjunction with certain lithography processes conducted with light having one or more wavelengths in the extreme ultraviolet (EUV) range (i.e., a EUV lithography process).
In order to accurately form minute circuit patterns on a semiconductor substrate using an EUV lithography process, it is necessary to precisely measure the phase of the constituent phase shift mask. At lower incident wavelengths, the phase of a phase shift mask may be accurately determined by dividing off a portion of phase impressioned light to a measurement circuit. Unfortunately, it is very difficult, if not practically impossible, to divide EUV light using conventional beam splitters. That is, because most of the EUV light is refracted from a beam splitter, a great portion of EUV light will not penetrate or pass through a beam splitter. Accordingly, the phase of the phase shift mask may not be effectively measured using the EUV light. As a result, the desired circuit pattern may not be correctly formed on a semiconductor substrate by using the phase shift mask.